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  1. #1
    Join Date
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    Default Back flattening - horse power rather than hand power

    Like many others on the forum I've been around the block with various methods of hand-powered flattening and I've looked for faster reliable methods.

    My first shot was on the side of a Tormek 10" wheel and it did a remarkable job on Mujingfang HSS plane blades that had shocking surface-grinding scratches. But once I'd used the cleaning stone to unclog the side it turned into a wimp.

    I also once tried a belt-sander upside down in a cradle but while it did bulk metal removal it didn't do flat.

    So here's a first test of an alternative:

    Tempered glass discs made by Worksharp along with their PSA abrasive discs*.

    While I have an MT2 arbour to go into the lathe (kindly made by a forum member) the shank was too wide for these discs. I made a cheap and cheerful alternative by cutting the head off a bolt with a long unthreaded section and mounted this in a jacobs chuck on the lathe.

    Not brilliant; a lot of run-out, but at 100 RPM the blade with finger pressure followed the surface.

    What you see in the pic is the rig with #80 on one side and #120 on the other.

    I used the lathe tool rest to position the tool but with a bit of practice it was unnecessary, so the rig could go into a drill press as well.

    The test tool was a sad-looking 1" Berg.

    The result was a flat back to 35mm back from the edge within minutes.

    I regularly reversed the lathe to avoid the leading side of the tool getting overworked.

    The abrasive** didn't readily clog though I brushed or rubber-sticked it clean often. Can't say how long it will last at this stage. Just by a finger drag from unused to used section, there was a distinct difference.

    After a bit of application some heat was transferred to the finger tip at which point I stopped and cleaned the disc.

    So all up it's looking very positive. I'm now looking for an MT2 arbour with a 12mm shank.

    Would a locally sourced alternative be a quality PSA abrasive mounted on an MDF disc? Possibly but haven't tried it; with backs in my book the mounting surface has to be as flat as you can get it. The WS discs checked with a quality straight edge are very flat. More so than diamond plates with hand power (1 thou variation can be expected; plate glass 1/100th; doesn't sound much but cumulative variation can give you a poor result). And quality coarse abrasive sheet seems only to be made by 3M (Imperial lapping film) and I'll shout a bottle of good fizz to anyone who can find a source of it in retail quantities.

    * WorkSharp is a tool sharpener from the US and it and its accessories when last I looked were not available in Aus. nor could the accessories be shipped to Aus.; I used the help of a kind US forum member to tranship the bits. (Correction, the whole kit is now available here from Carbatec but oh the price! Work Sharp™ System : CARBA-TEC )

    ** The abrasives I sourced run up to #1500. The #80 is Norton GI NO-FIL. The #120 is Norton NO-FIL SG A975 (assume SG = seeded gel which is top stuff). The #220 is Norton A275, NO-FIL Adalox (which I've also used from other sources for sanding turnings and performs well in that application).

    WS also sell a tempered glass disc with a leather covering and a green stick for fine honing.
    Cheers, Ern

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  3. #2
    Join Date
    Apr 2001
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    Perth
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    Default

    Hi Ern


    I did something similar (using aluminium) with velcro on one side, which attaches to the disk sander of my disk/belt sander combo. This spins at 1400 rpm, which is OK if you are careful. I also used this to flatten and polish the blades for marking knives, which are very thin.

    This is how I sharpen my lathe chisels, incidentally.

    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  4. #3
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    Good to hear of another option Derek.

    For flattening I'd be wary of the outcome of compressible mounting but maybe in that case the speed and a light touch would have helped.

    So I've continued with the rig and here's an update:

    Worked another 5 BE Berg backs from 3/4" down, and one 1/8" Berg mortice chisel. The 1/2" back was badly pitted and without HP I would've tossed it.

    The abrasive kept on doing the job but did slow down somewhat.

    The mortice was hard to keep on track not surprisingly and it will need finessing with a waterstone.

    But the work per piece is measured in minutes.

    There's a spare glass disc to which #180 and #220 abrasives will be applied to complete the flattening process. Then the tools will go on ceramic waterstones.

    All up, bl**dy brilliant.
    Cheers, Ern

  5. #4
    Join Date
    Jun 2010
    Location
    Canberra
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    195

    Default

    rssr, Similarly, I have tried the side of whetstone grinder and hand flattening on hard flat surfaces. I tried to do something similar to what you describe for coarse flattening of chisels using, instead of glass, a disk of melamine coated chipboard held with a central bolt in a power drill clamped to a bench. I use old floor sanding belts cut into rounds as the abrasive. I should have glued the belt onto the disk instead of just holding it with a large washer in the centre but didn't initially cos I thought it would wear out very quickly and it was more of an experiment to see how effective it was on hard steel. The abrasive disks last quite a long time however and can remove a large amount of metal. Their was a small amount of dubbing of the edges and part of this is due to fact the abrasive belts are very stiff and don't lie very flat, combined with the high speed of the drill and having to keep lifting if off and on to the surface to avoid overheating. I only tried it a couple of times and have mostly used it for reshaping the long bevel on mortice chisels (where accuracy is not critical) rather than for back flattening. I think the method would work a lot better for backs if I could slow down my drill speed (probably work great in a drill press) and glue the belt flat on the surface using a press with a suitable adhesive.

    Perfectionists would probably argue melamine coated chipboard itself is not flat enough but even with my shoddy experimental method followed by hand flattening I could go from the disk on the drill to a usable tool much quicker and without aching hands. I am converted!

  6. #5
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    My horsepower back-flattening technique is based on the WASP. I use silicon carbide belts running against a 100mm wide 6mm steel plate. It works very well.
    Cheers

    Jeremy
    If it were done when 'tis done, then 'twere well it were done quickly

  7. #6
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    May 2008
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    Allendale East, South Aus
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    Another thought. What about the abrasive of choice stuck onto a faceplate that has had the scraping treatment? I know myself and a few others on the forum have appropriate surface plates and blue dye at their disposal to flatten said faceplates. You wouldn't have any runout issues and mounting would be cake. The downside is that you would need a faceplate for each grit level of abrasive. Unless of course you made secondary alloy or thin plate steel plates the somehow mount to the faceplate itself, might be a lot cheaper than lots of faceplates but would be some meddling around making them.

    Tom.

  8. #7
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    Tom, hadn't thought of that. Checked my woodlathe faceplate, which is machined steel from Vicmarc I think, and it's as flat as the WS discs. With small batch production and PSA discs, it'd be a goer I reckon.

    Jeremy, anything special about your steel plate? Do you go up through the grits or flatten with one on the belt and move to a stone?

    Pampelmuse, yeah, I just scored some of that from a nature strip dump. Not the best source but anyway, it's variable but fairly flat and would do for the heavy lifting at say #80. And yes, I found that with the #80 WS PSA disc it didn't go down quite flat; needs a bit of practice (and 4 hands) to avoid trapping some air.

    Anyway, thanks all for sharing your approaches.
    Cheers, Ern

  9. #8
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    Just to add another poss. issue Pampelmuse with chipboard: it's prone to absorbing moisture so maybe it'd be worth sealing the cut edge to keep it, er, pristine?
    Cheers, Ern

  10. #9
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    Nothing really special about the plate, just make sure it is held securely and parallel to the WASP spindles. Mild steel is fine so long as it is basically flat since the real cutting surface is the belt.

    I start at 120 and go up through 200, 320 & 600 and then finish on my leather strop charged with diamond paste and baby oil
    Cheers

    Jeremy
    If it were done when 'tis done, then 'twere well it were done quickly

  11. #10
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    Thanks.

    Just a correction to the OP re the WS abrasives: the #1500 referred to is only 2 pieces of 2" square abrasive for lapping.

    And to add: the 80, 120 and 400 discs are ceramic oxide; the 220 and 1000 are Alox, and they also make 400 in Alox.
    Cheers, Ern

  12. #11
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    Update:

    Have just taken the batch of chisels to the next step, WS alox #220 and alox #400.

    They cut faster, hotter, clogged quicker and wore out quicker.

    Might as well whack on the #1000 discs much as the trad'l sharpener in me is itching to get to the stones

    Also found in the box of goodies from the US Micro-Mesh 3600 and 6000 discs.

    In for a penny ... but best do the bevels first.
    Cheers, Ern

  13. #12
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    Humph!

    Put a 20* bevel on the 1" chisel on the bench grinder and then returned to the rig with #1000 Alox abrasive to take the back to the next step.

    It cut slowly and clogged and wore quickly.

    I made the mistake of touching down on the edge after a change of rotation so thought sod it, to the waterstones.

    Job done after maybe half an hour all up with the #220 and #1000 Sigma Power Select IIs.

    Then while the kit was out took the rest of the chisels' backs to the #1000.

    Those cut fast but dish fast as well. I knew that; happy with the trade-off.
    Cheers, Ern

  14. #13
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    In an offline email conversation the issue was raised about overworking one side with power lapping.

    So just to report what the outcome of my process to #1000 was on the lathe-mounted discs:

    With a 1" BE Berg, the variation in thickness side to side is within 0.2 mm (not that the top is a reliable reference point). But there is some convexity on the bottom; by feeler gauge about 0.05mm. The discs are 6" running at 100 RPM reversing direction regularly .... the advantage of an EVS lathe.

    Next test will be lapping & polishing Thumbsucker's M2 plane blade. There are good reasons to expect more variation lapping that width.
    Cheers, Ern

  15. #14
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    Finally found a retail source of the coarse 3M microfinishing abrasives. Sticky and not sticky.

    Ideal for lapping backs with hand or horse power.

    Jewelry Making Supplies, Silver, Beads, Tools and Jewelry Packaging and Displays by Rio Grande.

    A bunch is winging its way across the Pacific. Shipping charge was very reasonable.
    Cheers, Ern

  16. #15
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    After spending the better part of a couple of evenings flattening the backs of my 5 new(ish) chisels, (I'm still not 100% happy as they have a bit to go yet). I can certainly say it's welcome to read about some of the power flattening options.

    Great find on the sticky abrasives. It has me wondering how hard it would be to make some sort of setup for the drill press that would be similar to the work mate systems... Surely the local glass cutter can cut some 10 or 12 mm round glass that we can fix abrasives too.

    I like the idea of hooking it up to a lathe, i'm just lacking a lathe How do you hold it when your flattening the back on a lathe? Would be interested to see a few pictures of your setup too.

    Cheers

    Simon

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